Signal modulation method, signal modulation apparatus, electronic device, and computer program product

ABSTRACT

A signal modulation method by an electronic device which includes a minimal reducing unit that minimally reduces an integrated signal returned to an adder from an integrator. 
     The signal modulation method includes generating an added signal with the adder. The signal modulation method further includes generating a new integrated signal with the integrator by returning a previously self-generated and stored integrated signal to the adder, and by integrating the added signal generated by the adder. 
     The signal modulation method further includes generating a new quantization signal with a quantizer by quantizing the new integrated signal generated by the integrator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a signal modulation method, a signalmodulation apparatus, an electronic device, and a computer programproduct.

2. Description of the Related Art

Signal modulation apparatuses (sigma-delta modulation apparatus anddelta-sigma modulation apparatus) that modulate an input signal, tocarry out an analog-digital conversion and a digital-analog conversionhave been widely applied to electronic devices such as audio equipment,communication equipment (for example, audio coder-decoder (CODEC) formobile terminals), and measuring equipment that require highly accuratesignal processing. Related technology has been disclosed in JapanesePatent Application Laid-open No. 2002-502565, Japanese PatentApplication Laid-open No. H07-7435, Japanese Patent ApplicationLaid-open No. 2002-314425, and Japanese Patent Application Laid-open No.2006-42315.

A related-art signal modulation apparatus will now be specificallyexplained with reference to FIG. 7. FIG. 7 is a schematic explanatorydiagram of the related-art signal modulation apparatus. The related-artsignal modulation apparatus that includes an adder, an integrator, and aquantizer (comparator), and that modulates an input signal to aquantization signal will be explained.

On receiving the input signal, the integrator of the related-art signalmodulation apparatus returns a previously self-generated and storedintegrated signal to the adder (see (1) in FIG. 7), and the quantizer ofthe related-art signal modulation apparatus returns a previouslyself-generated quantization signal to the adder (see (2) in FIG. 7).

The adder of the related-art signal modulation apparatus generates anadded signal, by subtracting the quantization signal returned by thequantizer from the input signal, and adding the integrated signalreturned by the integrator thereto (see (3) in FIG. 7).

The integrator of the related-art signal modulation apparatus generatesa new integrated signal by integrating the added signal generated by theadder, and stores the generated new integrated signal therein (see (4)in FIG. 7).

The quantizer of the related-art signal modulation apparatus generates anew quantization signal by quantizing the new integrated signalgenerated by the integrator (see (5) in FIG. 7).

In the related art, there is a problem that output noise generated byreceiving a silent signal cannot be reduced.

In other words, with the audio equipment and the audio CODEC that thesignal modulation apparatus is applied thereto, an improvement on thesignal to noise ratio (SN ratio) of the signal modulation apparatus, anda reduction of noise when the silent signal is received, are required toimprove the quality of actual sound.

However, in the related art that returns the integrated signal to theadder to improve the SN ratio of the signal modulation apparatus, when asilent signal is received after an audible signal is received as aninput signal, the integrated signal generated when the audible signal isreceived, is added to the silent signal. Therefore, an audiblequantization signal is generated, thereby occasionally generating noiseas a consequence. In the related art, even if the silent signal isreceived, the integrated signal generated when the audible signal isreceived, is repeatedly returned to the adder without being attenuated.Accordingly, noise is sometimes generated, even if the silent signal isreceived.

For example, with the related art that improves quality of actual soundby adding a random signal made of short bits to the input signal, asdisclosed in Japanese Patent Application Laid-open No. 2002-502565 andJapanese Patent Application Laid-open No. H07-7435, not only theinstallation is difficult, but noise is sometimes generated, even if therandom signal receives the silent signal.

SUMMARY

It is an object of the present invention to at least partially solve theproblems in the conventional technology.

According to an aspect of the present invention, a signal modulationmethod by an electronic device including a quantizer, an integrator, andan adder, includes generating an added signal with the adder bysubtracting a quantization signal returned by the quantizer from aninput signal and by adding an integrated signal returned by theintegrator to the input signal; generating a new integrated signal withthe integrator by returning a previously self-generated and storedintegrated signal to the adder and by integrating the added signalgenerated by the adder; generating a new quantization signal with aquantizer by quantizing the new integrated signal generated by theintegrator; and minimally reducing the integrated signal returned to theadder from the integrator.

According to another aspect of the present invention, a signalmodulation apparatus modulates an input signal to a quantization signal.The signal modulation apparatus includes a quantizer; an integrator; anadder that generates an added signal by subtracting the quantizationsignal returned by the quantizer from the input signal, and by adding anintegrated signal returned by the integrator to the input signal; and aminimal reducing unit. The integrator returns a previouslyself-generated and stored integrated signal to the adder, generates anew integrated signal by integrating the added signal generated by theadder, and stores therein the new integrated signal generated. Thequantizer returns a previously self-generated quantization signal to theadder, and generates a new quantization signal by quantizing the newintegrated signal generated by the integrator. The minimal reducing unitminimally reduces the integrated signal returned to the adder from theintegrator.

According to still another aspect of the present invention, anelectronic device modulates an input signal to a quantization signal.The electronic device includes a quantizer; an integrator; an adder thatgenerates an added signal by subtracting the quantization signalreturned by the quantizer from the input signal, and by adding anintegrated signal returned by the integrator to the input signal; and aminimal reducing unit. The integrator returns a previouslyself-generated and stored integrated signal to the adder, generates anew integrated signal by integrating the added signal generated by theadder, and stores therein the new integrated signal generated, thequantizer returns a previously self-generated quantization signal to theadder, and generates a new quantization signal by quantizing the newintegrated signal generated by the integrator, and the minimal reducingunit minimally reduces the integrated signal returned to the adder fromthe integrator.

According to still another aspect of the present invention, a computerprogram product having a computer readable medium including programmedinstructions that implement the above method on a computer.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic characteristic explanatory diagram of a signalmodulation apparatus according to a first embodiment of the presentinvention;

FIG. 2 is a block diagram of the signal modulation apparatus showing theconfiguration thereof;

FIG. 3 is a flowchart of a processing flow of the signal modulationapparatus;

FIG. 4 is a block diagram of the configuration of a CODEC macro;

FIG. 5 is a block diagram of the configuration of a mobile terminal;

FIG. 6 is a flowchart of a processing flow executed by a computer as thesignal modulation apparatus using a signal modulation program; and

FIG. 7 is a schematic explanatory diagram of a related-art signalmodulation apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of a signal modulation method, a signal modulationapparatus, an electronic device, and a signal modulation programaccording to the present invention will be described in detail belowwith reference to the accompanying drawings.

In a first embodiment, a schematic and characteristics of a signalmodulation apparatus, a configuration of the signal modulationapparatus, a processing flow of the signal modulation apparatusaccording to the first embodiment will be explained sequentially,followed by advantages of the first embodiment in the end. In the firstembodiment, a signal modulation apparatus (for example, sigma-deltamodulation apparatus) in which the invention is applied, and thatmodulates an input signal will be explained.

First, the schematic and characteristics of the signal modulationapparatus according to the first embodiment are explained with referenceto FIG. 1. FIG. 1 is a schematic characteristic explanatory diagram ofthe signal modulation apparatus according to the first embodiment.

The signal modulation apparatus according to the first embodimentincludes an adder that generates an added signal, an integrator thatintegrates the added signal, and a quantizer that quantizes anintegrated signal. The schematic of the signal modulation apparatusaccording to the first embodiment is to modulate an input signal to aquantization signal. The signal modulation apparatus according to thefirst embodiment also includes a minimal reducing unit between theintegrator and the adder. The main characteristic of the signalmodulation apparatus according to the first embodiment is to minimallyreduce the integrated signal returned to the adder from the integrator,by the minimal reducing unit. In this manner, the signal modulationapparatus according to the first embodiment can reduce output noisegenerated by receiving a silent signal.

More specifically, as shown in FIG. 1, the signal modulation apparatusaccording to the first embodiment, on receiving an input signal (see (1)in FIG. 1), generates an added signal (see (4) in FIG. 1) by using anintegrated signal (see (2) in FIG. 1) returned by the integrator, and aquantization signal (see (3) in FIG. 1) returned by the quantizer. Thesignal modulation apparatus according to the first embodiment thengenerates a new integrated signal (see (5) in FIG. 1) by integrating theadded signal, and generates a new quantization signal (see (6) inFIG. 1) by quantizing the new integrated signal.

At this time, the minimal reducing unit of the signal modulationapparatus according to the first embodiment generates a minimalreduction signal (see (7) in FIG. 1) that minimally reduces theintegrated signal from the integrated signal returned by the integrator,and minimally reduces the integrated signal returned to the adder fromthe integrator.

In this manner, the signal modulation apparatus according to the firstembodiment, as the main characteristic, can reduce the output noisegenerated by receiving the silent signal, by minimally reducing theintegrated signal returned to the adder from the integrator, by theminimal reducing unit.

A configuration of a signal modulation apparatus 10 will now beexplained with reference to FIG. 2. FIG. 2 is a block diagram of theconfiguration of the signal modulation apparatus. As shown in FIG. 2,the signal modulation apparatus 10 includes adders 11 a and 11 b,integrators 12 a and 12 b, minimal reducing units 13 a and 13 b, aquantizer 14, and a return value generator 15.

The adders 11 a and 11 b generate the added signals by subtracting thequantization signal returned by the quantizer 14 from the input signals,and by adding the integrated signal returned by the integrators 12 a and12 b to the input signals.

More specifically, the adder 11 a generates a first added signal bysubtracting the quantization signal returned by the quantizer 14 and afirst minimal reduction signal generated by the minimal reducing unit 13a, from the input signal input from outside of the signal modulationapparatus 10, and by adding a first integrated signal returned from theintegrator 12 a to the input signal.

The adder 11 b generates a second added signal by subtracting thequantization signal returned by the quantizer 14 and a second minimalreduction signal generated by the minimal reducing unit 13 b, from thenew first integrated signal generated by the integrator 12 a, and byadding a second integrated signal returned from the integrator 12 b tothe new first integrated signal.

The integrators 12 a and 12 b return the previously self-generated andstored integrated signal to the adders 11 a and 11 b, generate a newintegrated signal by integrating the added signal generated by theadders 11 a and 11 b, and store the generated new integrated signaltherein.

More specifically, the integrator 12 a returns the previouslyself-generated and stored first integrated signal to the adder 11 a andthe minimal reducing unit 13 a. The integrator 12 a then generates a newfirst integrated signal by integrating the first added signal generatedby the adder 11 a, and stores the generated new first integrated signaltherein.

The integrator 12 b returns the self-generated and stored secondintegrated signal to the adder 11 b and the minimal reducing unit 13 b.The integrator 12 b then generates a new second integrated signal byintegrating the second added signal generated by the adder 11 b, andstores the generated new second integrated signal therein.

The minimal reducing units 13 a and 13 b minimally reduce the integratedsignals returned to the adders 11 a and 11 b from the integrators 12 aand 12 b.

More specifically, on receiving the first integrated signal returnedfrom the integrator 12 a, the minimal reducing unit 13 a multiplies afirst coefficient by the first integrated signal, and generates a firstminimal reduction signal that minimally reduces the first integratedsignal.

On receiving the second integrated signal returned from the integrator12 b, the minimal reducing unit 13 b multiplies a second coefficient bythe second integrated signal, and generates a second minimal reductionsignal that minimally reduces the second integrated signal.

The first coefficient and the second coefficient will now be explainedin detail below. Symbol “z” indicates a variable. Symbol “Q” is a levelvalue of quantization noise generated when the integrated signal isquantized by the quantizer 14, as well as a real number. Symbol “*”indicates multiplication. Symbol “≅” (see Formula (3) and Formula (4))means approximately equal to.

A transfer function of the signal modulation apparatus that includes theadders 11 a and 11 b, the integrators 12 a and 12 b, the quantizer 14,and the return value generator 15, in other words, a so-called generalsecondary signal modulation apparatus, may be represented by Formula(1):

Input is a level value of the input signal, and Output is a level valueof the quantization signal. A signal transfer function (STF) is atransfer function of the signal, and a noise transfer function (NTF) isa transfer coefficient of noise.

In the signal modulation apparatus 10 according to the first embodiment,a transfer function of the signal modulation apparatus 10 according tothe first embodiment is represented by the following formula (2). Inthis formula, a first coefficient multiplied by the first integratedsignal, by the minimal reducing unit 13 a, is represented by α, and asecond coefficient multiplied by the second integrated signal, by theminimal reducing unit 13 b, is represented by β.

When the first coefficient a and the second coefficient β are assumed tosatisfy the following formula (3) and the formula (4) at the same time,the STF of the signal modulation apparatus 10 according to the firstembodiment becomes equal to the STF of the general secondary signalmodulation apparatus.α+β≅0  (3)α−β+αβ≅0  (4)

The NTF of the signal modulation apparatus 10 according to the firstembodiment may be modified to the following formula (5). When the firstcoefficient α and the second coefficient β satisfy Formula (3) andFormula (4) at the same time in the following formula (5), the NTF ofthe signal modulation apparatus 10 according to the first embodiment maybe represented by the following formula (6).

$\begin{matrix}\begin{matrix}{{NTF} = \frac{1 - {2\left( {2 - \alpha - \beta} \right)z^{- 1}} + {\left( {1 - \alpha - \beta + {\alpha\beta}} \right)z^{- 2}}}{1 + {\left( {\alpha + \beta} \right)z^{- 1}} + {\left( {\alpha - \beta + {\alpha\beta}} \right)z^{- 2}}}} \\{= {\frac{1 - \left\{ {{\left( {2 - \left( {\alpha + b} \right)} \right\} z^{- 1}} + {\left\{ {1 - {2\alpha} + \left( {a - \beta + {\alpha\beta}} \right)} \right\} z^{- 2}}} \right.}{1 + {\left( {\alpha + \beta} \right)z^{- 1}} + {\left( {\alpha - \beta + {\alpha\beta}} \right)z^{- 2}}}*Q}}\end{matrix} & (5) \\{{NTF} = {\frac{1 - {2z^{- 1}} + z^{- 2} - {2\alpha\; z^{- 2}}}{1} = {\left( {1 - z^{- 1}} \right)^{2} - {2\alpha\; z^{- 2}}}}} & (6)\end{matrix}$

In other words, the signal modulation apparatus 10 according to thefirst embodiment does not affect the level value of the Input, when theInput is an audible signal. When the Input is a silent signal, thesignal modulation apparatus 10 according to the first embodiment mayreduce the integrated signal returned to the adder 11 a from theintegrator 12 a by α, and may reduce the integrated signal returned tothe adder 11 b from the integrator 12 b by β.

For example, the signal modulation apparatus 10 according to the firstembodiment, when “α” and “β” are 2 to the minus 16th power, can reducethe integrated signal returned to the adder 11 a from the integrator 12a by a value multiplied by 2 to the minus 16th power, every time thesilent signal is received. As a result, the quantization noise can bereduced by a value, z−2 (this represents an index of −2 with respect toa base, z) is multiplied by 2 to the minus 15th power, than the generalsecondary signal modulation apparatus.

The quantizer 14 generates a new quantization signal by returning thepreviously self-generated quantization signal to the adders 11 a and 11b, and quantizing the new integrated signal generated by the integrator12 b. More specifically, the quantizer 14 returns the previouslyself-generated quantization signal to the adders 11 a and 11 b via thereturn value generator 15. The quantizer 14 then generates a newquantization signal by quantizing the new integrated signal generated bythe integrator 12 b, outputs the quantization signal to outside of thesignal modulation apparatus 10, and stores the generated newquantization signal therein.

The return value generator 15 converts the quantization signal returnedby the quantizer 14. More specifically, the return value generator 15converts the quantization signal returned by the quantizer 14, in a formof signal to be subtracted from the input signal, in the adder 11 a orthe adder 11 b, respectively. For example, when the input signal inputinto the adder 11 a is set to 16 bits, and the quantization signalreturned by the quantizer 14 is set to 1 bit, the return value generator15 converts the quantization signal to 16 bits.

A processing flow of the signal modulation apparatus 10 will now beexplained with reference to FIG. 3. FIG. 3 is a flowchart of theprocessing flow of the signal modulation apparatus. The processing to beexplained below is repeatedly executed while the signal modulationapparatus 10 is activated, and will be finished when the signalmodulation apparatus 10 stops activating.

As shown in FIG. 3, on receiving an input signal input from outside (Yesat step S1001), the signal modulation apparatus 10 returns a firstintegrated signal and a quantization signal (step S1002). Morespecifically, the integrator 12 a returns the previously self-generatedand stored first integrated signal to the adder 11 a and the minimalreducing unit 13 a, and the quantizer 14 returns the previouslyself-generated and stored quantization signal to the adder 11 a.

The signal modulation apparatus 10 generates a first minimal reductionsignal and coverts the quantization signal (step S1003). Morespecifically, the minimal reducing unit 13 a generates the first minimalreduction signal, and the return value generator 15 converts thequantization signal in a form to be subtracted in the adder 11 a.

The signal modulation apparatus 10 generates a first added signal (stepS1004). More specifically, the adder 11 a generates the first addedsignal by subtracting the quantization signal returned by the quantizer14 and the first minimal reduction signal generated by the minimalreducing unit 13 a, from the input signal, and by adding the firstintegrated signal returned from the integrator 12 a to the input signal.

The signal modulation apparatus 10 generates a first integrated signal(step S1005), and stores the first integrated signal therein (stepS1006). More specifically, the integrator 12 a generates a new firstintegrated signal by integrating the first added signal, and stores thegenerated new first integrated signal therein.

The signal modulation apparatus 10 returns a second integrated signaland the quantization signal (step S1007). More specifically, theintegrator 12 b returns the previously self-generated and stored secondintegrated signal to the adder 11 b and the minimal reducing unit 13 b.The quantizer 14 returns the previously self-generated and storedquantization signal to the adder 11 b.

The signal modulation apparatus 10 generates a second minimal reductionsignal and converts the quantization signal (step S1008). Morespecifically, the minimal reducing unit 13 b generates the secondminimal reduction signal, and the return value generator 15 converts thequantization signal in a form to be subtracted in the adder 11 b.

The signal modulation apparatus 10 generates a second added signal (stepS1009). More specifically, the adder 11 b generates the second addedsignal by subtracting the quantization signal returned by the quantizer14 and the second minimal reduction signal generated by the minimalreducing unit 13 b, from the new first integrated signal, and by addingthe second integrated signal returned from the integrator 12 b to theinput signal.

The signal modulation apparatus 10 generates a second integrated signal(step S1010), and stores the second integrated signal therein (stepS1011). More specifically, the integrator 12 b generates a new secondintegrated signal by integrating the second added signal, and stores thegenerated new second integrated signal therein.

The signal modulation apparatus 10 generates a quantization signal (stepS1012), outputs the quantization signal (step S1013), stores thequantization signal therein (step S1014), and waits again for the inputsignal (step S1001). More specifically, the quantizer 14 generates a newquantization signal by quantizing the new integrated signal generated bythe integrator 12 b, outputs the quantization signal to outside of thesignal modulation apparatus 10, and stores the generated newquantization signal therein.

According to the first embodiment, it is possible to reduce the outputnoise generated by receiving the silent signal, because the integratedsignal returned to the adder from the integrator is minimally reduced.

According to the first embodiment, it is also possible to reduce theoutput noise generated by receiving the silent signal in the secondarysignal modulation apparatus. This is because the first integrated signalreturned to the first adder from the first integrator is minimallyreduced, and the second integrated signal returned to the second adderfrom the second integrator is minimally reduced.

According to the first embodiment, a user may arbitrarily setpredetermined coefficients α and β that satisfy Formula (3) and Formula(4) at the same time. This is because the first integrated signal isminimally reduced, by multiplying a predetermined coefficient α thatsatisfies Formula (3) and Formula (4) at the same time by the firstintegrated signal, and the second integrated signal is minimallyreduced, by multiplying a predetermined coefficient β that satisfiesFormula (3) and Formula (4) at the same time by the second integratedsignal.

In the first embodiment, the signal modulation apparatus 10 in which theinvention is applied, and which modulates the input signal wasexplained. The signal modulation apparatus 10 according to the presentinvention can be mounted on electronic devices that modulates an analogsignal to a digital signal, and a digital signal to an analog signal(for example, CODEC macro). In a second embodiment, when the signalmodulation apparatus 10 according to the first embodiment is applied tothe CODEC macro will be explained. The CODEC macro modulates the analogsignal to the digital signal, and the digital signal to the analogsignal. In the second embodiment, a configuration of the CODEC macroaccording to the second embodiment will be explained, followed by theadvantages of the second embodiment.

A configuration of a CODEC macro 20 according to a second embodimentwill now be explained with reference to FIG. 4. FIG. 4 is a blockdiagram of the configuration of a CODEC macro.

As shown in FIG. 4, the CODEC macro 20 includes an analog-digitalconverter 21 and a digital-analog converter 22. The analog-digitalconverter 21 includes a pre-filter 23, a signal modulation apparatus 10a, and a digital filter 24 a to convert an analog signal to a digitalsignal. It will be explained under the assumption that the pre-filter 23and the signal modulation apparatus 10 a execute each processing byhardware processing, and the digital filter 24 a executes the processingby software processing that executes a predetermined algorithm on acomputer.

The pre-filter 23 corresponds to a low-pass filter that removes afrequency band equal to or more than a predetermined frequency from theinput signal, and anti-aliases the analog signal. In other words, thepre-filter 23 suppresses folded noise generated by the signal modulationapparatus 10 a.

In other words, when an analog signal that includes a higher frequencysignal than a Nyquist frequency (fs/2), which is a half of a samplingfrequency (fs), is modulated into a digital signal by the signalmodulation apparatus 10 a, it is possible that the folded noise isincluded in the modulated digital signal. For example, when an analogsignal of 1.1 megahertz is modulated into a digital signal, by thesignal modulation apparatus 10 a of which the sampling frequency is 2megahertz and the Nyquist frequency is 1 megahertz, the analog signal ismodulated into the digital signal of 0.9 megahertz. The digital signalof 0.9 megahertz is noise that is not included in the analog signalbefore being modulated, and is called folded noise. The pre-filter 23suppresses the generation of such folded noise.

The signal modulation apparatus 10 a modulates the analog signal to thedigital signal. More specifically, the signal modulation apparatus 10 acorresponds to the signal modulation apparatus 10 according to the firstembodiment. The signal modulation apparatus 10 a minimally reduces theintegrated signal returned to the adders 11 a and 11 b from theintegrators 12 a and 12 b, by the same process as that of the signalmodulation apparatus 10 according to the first embodiment. Moreover, thesignal modulation apparatus 10 a modulates the analog signalanti-aliased by the pre-filter 23 to the digital signal.

The digital filter 24 a down-samples the digital signal. Morespecifically, the digital filter 24 a corresponds to a decimationfilter, and reduces the sampling frequency of the digital signalmodulated by the signal modulation apparatus 10 a. The digital filter 24a is formed by a high-pass filter and a low-pass filter, and restrictsthe frequency band of the digital signal modulated by the signalmodulation apparatus 10 a.

The digital-analog converter 22 includes a post-filter 25, a signalmodulation apparatus 10 b, and a digital filter 24 b, to modulate thedigital signal to the analog signal. It will be explained under theassumption that the post-filter 25 executes the processing by thehardware processing, and the signal modulation apparatus 10 b and thedigital filter 24 b execute each processing by the software processingthat executes a predetermined algorithm on a computer.

The digital filter 24 b up-samples the digital signal. Morespecifically, the digital filter 24 b corresponds to an interpolationfilter, and increases the sampling frequency of the digital signal inputinto the CODEC macro 20. The digital filter 24 b is formed by ahigh-pass filter and a low-pass filter, and restricts the frequency bandof the digital signal input into the CODEC macro 20.

The signal modulation apparatus 10 b modulates the digital signal to theanalog signal. More specifically, the signal modulation apparatus 10 bcorresponds to the signal modulation apparatus 10 according to the firstembodiment. The signal modulation apparatus 10 b minimally reduces theintegrated signal returned to the adders 11 a and 11 b from theintegrators 12 a and 12 b, by the process opposite to the signalmodulation apparatus 10 according to the first embodiment. The signalmodulation apparatus 10 b also modulates the digital signal of which thefrequency is increased by the digital filter 24 b to the analog signal.

The post-filter 25 removes a component of the signal equal to or morethan a predetermined frequency from the analog signal. Morespecifically, the post-filter 25 corresponds to the low-pass filter, andremoves the noise equal to or more than a predetermined frequencygenerated by the digital-analog conversion by the signal modulationapparatus 10 b, from the analog signal.

According to the second embodiment, it is possible to apply theinvention to the CODEC macro that modulates the analog signal to thedigital signal, and the digital signal to the analog signal. It is alsopossible to reduce the output noise generated when the silent analogsignal and the silent digital signal are received.

According to the second embodiment, it is possible to apply theinvention to the CODEC macro that includes the signal modulationapparatus that modulates the analog signal to the digital signal byhardware processing using an electric circuit, and the signal modulationapparatus that modulates the digital signal to the analog signal bysoftware processing that executes a predetermined algorithm on acomputer.

In the second embodiment, when the signal modulation apparatus 10according to the present embodiment is applied to the CODEC macro 20 wasexplained. The CODEC macro 20 applied with the signal modulationapparatus 10 according to the present invention can be mounted onelectronic devices such as audio equipment, communication equipment(audio CODEC), and measuring equipment that require highly accuratesignal processing. In a third embodiment, when the CODEC macro accordingto the second embodiment is mounted on a mobile terminal will beexplained. In the third embodiment, a configuration of the mobileterminal according to the third embodiment will be explained, followedby the advantages of the third embodiment.

A configuration of a mobile terminal according to the third embodimentwill now be explained with reference to FIG. 5. FIG. 5 is a blockdiagram of the configuration of the mobile terminal.

As shown in FIG. 5, a mobile terminal 30 includes the CODEC macro 20, ananalog signal input unit 31, an analog signal output unit 32, an antenna33, a digital base band (DBB) macro 34, and an application (APL) chip36.

The CODEC macro 20 modulates the analog signal to the digital signal,and the digital signal to the analog signal. More specifically, theCODEC macro 20 corresponds to the CODEC macro 20 according to the secondembodiment, modulates the analog signal to the digital signal by theanalog-digital converter 21, and modulates the digital signal to theanalog signal by the digital-analog converter 22.

The analog signal input unit 31 receives the analog signal from outsideof the mobile terminal 30. More specifically, the analog signal inputunit 31 corresponds to an analog terminal that receives the analogsignal (such as sound-collecting microphone, headphone, hands-freedevice, and Bluetooth®), and for example, receives sound outputted by auser.

The analog signal output unit 32 outputs the analog signal to outside ofthe mobile terminal 30. More specifically, the analog signal output unit32 corresponds to an analog terminal that outputs the analog signal(such as output speaker, headphone, hands-free device, and Bluetooth®),and for example, outputs sound to the user.

The antenna 33 transmits and receives a signal. More specifically, theantenna 33 transmits a wireless signal to a base station from the mobileterminal 30, and receives the wireless signal transmitted to the mobileterminal 30 from the base station.

The DBB macro 34 executes communication processing of variousinformation. More specifically, a transmission/reception processing unit35 of the DBB macro 34 transmits and processes a wireless signal thatincludes various digital transmission data (such as a wireless signalthat includes audio data and a wireless signal that includes informationdata received from the CODEC macro 20) via the antenna 33. Thetransmission/reception processing unit 35 of the DBB macro 34 alsoseparates reception data included in the wireless signal received viathe antenna 33 to various digital reception data, and transfers to eachmacro (including macro not shown) provided in the mobile terminal 30.For example, when the wireless signal that includes audio data isreceived via the antenna 33, the transmission/reception processing unit35 of the DBB macro 34 transfers the digital signal that includes theaudio data to the CODEC macro 20.

The APL chip 36 controls each macro (including macro not shown) providedin the mobile terminal 30. More specifically, the APL chip 36corresponds to a central processing unit (CPU) that executes variousapplications. The APL chip 36 controls the process of modulating theanalog signal to the digital signal and modulating the digital signal tothe analog signal by the CODEC macro 20, and controls the communicationprocessing of various information by the DBB macro 34.

According to the third embodiment, it is possible to mount the CODECmacro 20 according to the second embodiment on the mobile terminal 30,and it is also possible to reduce the output noise during silenceperiod.

The first to the third embodiments have been explained, but the presentinvention may be applied to various modifications other than theembodiments described above. Other embodiments will be explained belowas a fourth embodiment.

For example, in the first embodiment, it was explained that “α” and “β”are 2 to the minus 16th power. The “α” and the “β” are coefficientsmultiplied by the integrated signal returned to the adders 11 a and 11 bfrom the integrators 12 a and 12 b by the minimal reducing units 13 aand 13 b. However, the present invention is not limited to this, and thepresent invention can be applied when the first coefficient α and thesecond coefficient β satisfy Formula (3) and Formula (4) at the sametime. For example, α may be 2 to the minus 16th power, and β may be zero(0).

In the first embodiment, it was explained that the minimal reductionsignal that minimally reduces the integrated signal is generated, bymultiplying a predetermined coefficient by the integrated signal,returned to the adders 11 a and 11 b from the integrators 12 a and 12 b,by the minimal reducing units 13 a and 13 b. However, the presentinvention is not limited to this, and the present invention may beapplied when the minimal reduction signal that minimally reduces theintegrated signal is generated. For example, a minimal reduction signalwith the same code (for example, a certain level signal at about a leastsignificant bit (LSB) of the bit width of the adder in a digital circuitconfiguration) may be generated, by determining the code of informationincluded in the integrated signal.

In the first embodiment, when the present invention is applied to thesecondary signal modulation apparatus 10 was explained. However, thepresent invention is not limited to this. For example, even with thesignal modulation apparatus 10 of n-order, or with the signal modulationapparatus that improves quality of actual sound by adding a randomsignal made of short bits to the input signal, the present invention canbe applied by changing the coefficient multiplied by the integratedsignal.

In the second embodiment, it was explained that the pre-filter 23, thesignal modulation apparatus 10 a, and the post-filter 25 execute eachprocessing by the hardware processing, and the signal modulationapparatus 10 b and the digital filters 24 a and 24 b execute theprocessing by the software processing that executes a predeterminedalgorithm on a computer. However, the present invention is not limitedto this, and for example, all the processing may be executed by thehardware processing or all the processing may be executed by thesoftware processing.

The processing procedures, the control procedures, specific names, andvarious data shown in the specification or in the drawings explained inthe present embodiments can be optionally changed, unless otherwisespecified.

The respective constituents of the respective apparatuses shown in FIGS.2, 4, and 5 are functionally conceptual, and need not be physicallyconfigured as illustrated. In other words, the specific mode ofdispersion and integration of each apparatus is not limited to theillustrations, and all or a part thereof can be functionally orphysically dispersed or integrated in an optional unit, depending onvarious loads and the status of use.

For example, in FIG. 2, the integrator 12 a is configured to return thepreviously self-generated and stored first integrated signal to theadder 11 a and the minimal reducing unit 13 a. However, the integrator12 a may be configured, so as to convert the first integrated signalwith respect to the adder 11 a, by returning the first integrated signalto the minimal reducing unit 13 a, and by having the minimal reducingunit 13 a to minimally reduce the first integrated signal. Moreover, inFIG. 4, the signal modulation apparatus 10 a and the digital filter 24 amay be integrated, and in FIG. 5, the CODEC macro 20 and the APL chip 36may be integrated.

All or an optional part of each processing function carried out in eachapparatus may be realized by the CPU, a micro controller unit (MCU), amicro processing unit (MPU), and a program analyzed and executed by theCPU, the MCU, and the MPU, or may be realized as hardware by wiredlogic.

The signal modulation method explained in the present embodiment may berealized by executing a program prepared in advance on a computer suchas a personal computer and a work station.

A signal modulation program that allows a computer to execute the signalmodulation method that modulates the input signal to the quantizationsignal will now be explained with reference to FIG. 6. The computer asthe signal modulation apparatus includes the adder that generates theadded signal, the integrator that integrates the added signal, thequantizer that quantizes the integrated signal, and the minimal reducingunit that minimally reduces the integrated signal returned to the adderfrom the integrator. FIG. 6 is a flowchart of a processing flow executedby the computer as the signal modulation apparatus using the signalmodulation program.

As shown in FIG. 6, the computer as the signal modulation apparatusdetermines whether an interruption to finish the process is made, whenthe signal modulation program is activated (step S2001).

When it is determined that an interruption to finish the process is notmade (No at step S2001), the computer as the signal modulation apparatusdetermines whether an input signal is received (step S2002).

When it is determined that the input signal is not received (No at stepS2002), the computer as the signal modulation apparatus determineswhether an interruption to finish the process is made (step S2001).

On determining that the input signal is received (Yes at step S2002),the computer as the signal modulation apparatus reads out the levelvalue of the integrated signal previously generated by the integratorfrom a predetermined storage unit, and reads out the level value of thequantization signal previously generated by the quantizer from apredetermined storage unit (step S2003). When the process of reading outthe level values of the integrated signal and the quantization signalfrom a predetermined storage unit is executed for the first time,initial values (such as zero) of the integrated signal and thequantization signal set by a user will be read out from a predeterminedstorage unit.

The computer as the signal modulation apparatus calculates a minimalreduction value that minimally reduces the level value of the integratedsignal, and converts the level value of the quantization signal in thelevel value to be subtracted by the adder (step S2004).

The computer as the signal modulation apparatus calculates the levelvalue of the added signal by subtracting the minimal reduction value andthe level value of the converted quantization signal from the levelvalue of the input signal, and by adding the level value of theintegrated signal to the level value of the input signal (step S2005).

The computer as the signal modulation apparatus calculates the levelvalue of the new integrated signal from the level value of the addedsignal (step S2006), and calculates the level value of the newquantization signal from the level value of the new integrated signal(step S2007).

The computer as the signal modulation apparatus outputs the quantizationsignal based on the level value of the calculated new quantizationsignal (step S2008), and stores the level value of the calculated newintegrated signal and the level value of the new quantization signal ina predetermined storage unit (step S2009).

The computer as the signal modulation apparatus again determines whetheran interruption to finish the process is made (step S2001), andrepeatedly executes the processes (steps S2001 to S2009), until aninterruption to finish the process is made (Yes at step S2001).

The signal modulation program can be distributed via a network such asthe Internet. The signal modulation program may be stored incomputer-readable storage media such as hard disk, flexible disk (FD),compact disk read-only memory (CD-ROM), magneto optical disk (MO), anddigital versatile disk (DVD), and may be executed by being read out fromthe storage medium by a computer.

According to an embodiment of the present invention, the output noisegenerated by receiving the silent signal can be reduced.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

1. A signal modulation method by an electronic device including aquantizer, an integrator, and an adder, the method comprising:generating an added signal with the adder by subtracting a quantizationsignal returned by the quantizer from an input signal and by adding anintegrated signal returned by the integrator to the input signal;generating a new integrated signal with the integrator by returning apreviously self-generated and stored integrated signal to the adder andby integrating the added signal generated by the adder; generating a newquantization signal with a quantizer by quantizing the new integratedsignal generated by the integrator; and minimally reducing theintegrated signal returned to the adder from the integrator.
 2. Thesignal modulation method according to claim 1, wherein the adderincludes a first adder and a second adder, and the integrator includes afirst integrator and a second integrator, the method further comprising:generating a first added signal by subtracting the quantization signalreturned by the quantizer from the input signal and by adding a firstintegrated signal returned from the first integrator to the inputsignal; generating and storing a new first integrated signal with thefirst integrator by returning a previously self-generated and storedfirst integrated signal to the first adder and by integrating the addedsignal generated by the first adder; generating a second added signal bysubtracting the quantization signal returned by the quantizer from thenew first integrated signal and by adding a second integrated signalreturned from the second integrator to the first integrated signal;generating and storing a new second integrated signal with the secondintegrator by returning a previously self-generated and stored secondintegrated signal to the second adder and by integrating the addedsignal generated by the second adder; generating a new quantizationsignal with the quantizer by quantizing the new integrated signalgenerated by the second integrator; minimally reducing the firstintegrated signal returned to the first adder from the first integrator;and minimally reducing the second integrated signal returned to thesecond adder from the second integrator.
 3. The signal modulation methodaccording to claim 2, wherein the minimally reducing the firstintegrated signal includes minimally reducing the first integratedsignal by multiplying a predetermined coefficient α by the firstintegrated signal, and the minimally reducing the second integratedsignal includes minimally reducing the second integrated signal bymultiplying a predetermined coefficient β by the second integratedsignal,where α+β≅0 and α−β+αβ≅0.
 4. The signal modulation method according toclaim 1, wherein the electronic device includes a first signalmodulation apparatus that modulates an analog signal to a digitalsignal, and a second signal modulation apparatus that modulates adigital signal to an analog signal, the method comprising: causing thefirst signal modulation apparatus to execute the minimal reduction byany one of or both hardware processing using an electric circuit andsoftware processing that executes a predetermined algorithm on acomputer; and causing the second signal modulation apparatus to executethe minimal reduction by any one of or both hardware processing using anelectric circuit and software processing that executes a predeterminedalgorithm on the computer.
 5. A signal modulation apparatus thatmodulates an input signal to a quantization signal, the signalmodulation apparatus comprising: a quantizer; an integrator; an adderthat generates an added signal by subtracting the quantization signalreturned by the quantizer from the input signal, and by adding anintegrated signal returned by the integrator to the input signal; and aminimal reducing unit, wherein the integrator returns a previouslyself-generated and stored integrated signal to the adder, generates anew integrated signal by integrating the added signal generated by theadder, and stores therein the new integrated signal generated, thequantizer returns a previously self-generated quantization signal to theadder, and generates a new quantization signal by quantizing the newintegrated signal generated by the integrator, and the minimal reducingunit minimally reduces the integrated signal returned to the adder fromthe integrator.
 6. An electronic device that modulates an input signalto a quantization signal, the electronic device comprising: a quantizer;an integrator; an adder that generates an added signal by subtractingthe quantization signal returned by the quantizer from the input signal,and by adding an integrated signal returned by the integrator to theinput signal; and a minimal reducing unit, wherein the integratorreturns a previously self-generated and stored integrated signal to theadder, generates a new integrated signal by integrating the added signalgenerated by the adder, and stores therein the new integrated signalgenerated, the quantizer returns a previously self-generatedquantization signal to the adder, and generates a new quantizationsignal by quantizing the new integrated signal generated by theintegrator, and the minimal reducing unit minimally reduces theintegrated signal returned to the adder from the integrator.
 7. Theelectronic device according to claim 6, wherein the adder includes afirst adder and a second adder, the integrator includes a firstintegrator and a second integrator, and the minimal reducing unitincludes a first minimal reducing unit and a second minimal reducingunit, wherein the first adder generates a first added signal bysubtracting the quantization signal returned by the quantizer from theinput signal, and by adding a first integrated signal returned from thefirst integrator to the input signal, the first integrator returns apreviously self-generated and stored first integrated signal to thefirst adder, generates a new first integrated signal by integrating thefirst added signal generated by the first adder, and stores therein thenew first integrated signal thus generated, the second adder generates asecond added signal by subtracting the quantization signal returned bythe quantizer from the new first integrated signal generated by thefirst integrator, and by adding a second integrated signal returned froma second integrator to the new first integrated signal generated, thesecond integrator returns a previously self-generated and stored secondintegrated signal to the second adder, generates a new second integratedsignal by integrating the second added signal generated by the secondadder, and stores therein the new second integrated signal generated,the quantizer returns a previously self-generated quantization signal tothe first adder and the second adder, and generates a new quantizationsignal by quantizing the new second integrated signal generated by thesecond integrator, the first minimal reducing unit minimally reduces thefirst integrated signal returned to the first adder from the firstintegrator, and the second minimal reducing unit minimally reduces thesecond integrated signal returned to the second adder from the secondintegrator.
 8. The electronic device according to claim 7, wherein thefirst minimal reducing unit minimally reduces the first integratedsignal by multiplying a predetermined coefficient α by the firstintegrated signal, and the second minimal reducing unit minimallyreduces the second integrated signal by multiplying a predeterminedcoefficient β by the first integrated signal,where α+β≅0 and α−β+αβ≅0.